The present invention relates to a device for turning on light, and more particularly to an inverter-type device for turning on light and an inverter-type illumination apparatus.
Recently, an inverter-type illumination apparatus, which converts the DC voltage obtained from the commercial AC voltage to a high-frequency AC voltage for application to a discharge tube, has been widely used. The discharge tube of this illumination apparatus may be a standard fluorescent lamp with a filament or a non-electrode fluorescent lamp without a filament in which a plasma is generated by the line of magnetic force emitted from an excitation coil. It is known that this type of inverter-type illumination apparatus has a light adjustment function. For example, the circuit for turning on light disclosed in JP-A-8-37092 changes the frequency of the AC current, supplied to the resonance circuit, to change the amount of current flowing into the discharge tube for brightness adjustment.
The conventional device for turning on light described above uses a variable-frequency oscillation circuit, which generates the square wave of a desired frequency, to change the frequency of the current to be supplied to the resonance circuit. This additional circuit increases the number of parts and the cost. In addition, changing the frequency in order to change the brightness of the illumination apparatus requires the user to operate the device for turning on light within the illumination apparatus. Therefore, the brightness of the illumination apparatus cannot be adjusted remotely.
It is an object of the present invention to provide a function to adjust the brightness of an inverter-type illumination apparatus without having to install an additional oscillation circuit. It is another object of the present invention to provide a function to remotely adjust the brightness of an inverter-type illumination apparatus.
The above objects are achieved by a device for turning on light comprising DC (Direct Current) voltage generating means for generating a DC voltage from a commercial AC (Alternate Current) voltage; and first switching means for switching the generated DC current and for supplying a high-frequency current to a discharge tube via first resonance circuit means which includes a capacitor connected in parallel with the discharge tube to be lighted and whose resonance frequency is determined according to an equivalent impedance of the discharge tube, wherein the DC voltage generating means has control means for adjusting a value of the DC voltage and wherein a switching of the switching means is controlled by a phase of a resonance current flowing through the first resonance circuit means.
When the DC voltage supplied to the first switching means is changed to change the amplitude of the high-frequency AC voltage in the device for turning on light, the value of the current flowing through the discharge tube also changes. Because the discharge tube has negative resistance characteristics, the equivalent impedance of the discharge tube also changes. Therefore, the resonance frequency of the first resonance circuit changes accordingly, the switching frequency of the first switching means changes, and the frequency of the AC current flowing through the first resonance circuit changes. When the frequency of the AC current changes, the impedance of the capacitor in parallel with the discharge tube changes, the ratio between the current flowing through the discharge tube and the current flowing through the capacitor changes, and the brightness of the discharge tube changes. That is, simply changing the DC voltage to be supplied to the first switching means automatically changes the frequency of the high-frequency AC current supplied to the resonance circuit and the discharge tube, changing the current flowing through the discharge tube, thus changing the brightness. Therefore, an additional oscillator defining the switching frequency of the switching means required in the conventional device is no more needed.
The first switching means comprises two switching elements which are alternately conducted or non-conducted when a control signal obtained from the resonance current flowing through the first resonance circuit means is applied, the two switching elements connected in series; and means for changing a phase of the control signal. Controlling the timing in which the switching elements conduct prevents the switching elements from being heated by the charge and discharge of the parasitic capacitance.
The DC voltage generating means comprises a first capacitor which receives a current from the commercial AC voltage to establish the DC voltage; and second switching means for supplying the current from the commercial AC voltage to second resonance circuit means and for moving a charge accumulated in the second resonance means to the first capacitor, wherein the second switching means and the first switching means are the same. This configuration enables the DC voltage supplied to the switching means to be amplified.
The above objects are achieved by a device for turning on light with a communication function, comprising an inverter generating a high-frequency current from a commercial AC voltage supplied from a lamp line and supplying the current to a discharge tube to be lighted; and a communication interface communicating with external units via the lamp line, wherein the inverter comprises DC voltage generating means for generating a DC voltage from the commercial AC voltage supplied from the lamp line; switching means for switching the generated DC voltage and for supplying the high-frequency current to the discharge tube via a resonance circuit including a capacitor connected in parallel with the discharge tube; and driving circuit means for controlling the switching of the switching means based on a signal supplied from external sources, and wherein the communication interface comprises filter means for extracting from the commercial AC voltage an analog signal including lighting control information and superposed on the commercial AC voltage; means for generating a digital control signal sending at least one of switching start information, switching stop information, and switching frequency information to the driving circuit means based on information from the filter means; and lighting control means for sending the digital control signal to the driving circuit means.
Sending a signal from external units to this device for turning on light with a communication function allows the frequency of the AC voltage applied to the discharge tube to be changed, thus making it possible to remotely adjust the brightness of the discharge tube.
The inverter further comprises a first sensor generating lighting state information as a digital lighting state signal and wherein the communication interface converts the digital lighting state signal, received from the first sensor, to an analog signal and superposes the signal on the commercial AC voltage for transmission to external units via the lamp line. In addition, the inverter further comprises a second sensor detecting a presence of and a life running-down state of the discharge tube and wherein the communication interface converts the digital lighting state signal, including information detected by the first sensor and second sensor, to an analog signal, superposes the signal on the commercial AC voltage, and transmits the signal to external units via the lamp line. This makes the management and maintenance of the illumination apparatus more efficient.
The lighting control means further comprises storing means for storing therein a control pattern controlling the discharge tube in such a way that the discharge tube is lighted at a maximum luminous flux for a predetermined time after a start of lighting and, after the predetermined time, at a luminous flux lower than the maximum luminous flux. This allows the user to use the illumination apparatus more efficiently and reduces the power consumption.